The present invention relates to signal switching devices usable in the switching network of automatic telephone exchanges, and more particularly to those located on the subscriber or trunk terminals of the switching network and employing electromagnetic switching elements.
Signal switching devices of the kind described comprise an input and output signal line electromagnetic switching matrix which includes switching elements arranged at the points of intersection between a multitude of input signal lines and a multitude of output signal lines intersecting the input signal lines substantially at right angles thereto. These switching devices serve the purpose of switcing the input and output signal lines upon the application of control signals to the input and output control lines thereby to electromagnetically open and close the electromagnetic switching elements. A cutoff circuit is arranged to connect the call detector circuit with or disconnect it from the input signal lines and/or an off-normal circuit for preventing any interruption of direct currents due to operation of the switching elements in the switching matrix.
In the manufacture of switching devices of the kind described, conventional practice has been to design and fabricate a switching matrix, a cutoff circuit and/or an off-normal circuit independently from each other. This practice, however, has many disadvantages, includng limited use of parts in common to the different component circuits, increase in the number of individual parts required, need for wiring between the switching matrix and the circuits, and an increase in the cost of fabrication of the switching network as a whole. Moreover, this practice has precluded any substantial reduction in size, weight and fabrication cost of the device.